Turn off the circuit breaker to the FireX smoke alarm. The circuit breaker for the smoke alarm is in your home electrical box.
Place a step stool under the FireX smoke alarm so you can reach it. Grab the body of the smoke detector, and turn it counterclockwise until it disengages from the mounting plate.
Lower the smoke alarm until you are able to access the power harness. The power harness is the connector that plugs into the smoke detector.
Grab the power harness connector with your fingers, and pull it out of the smoke alarm. Maintain a firm grasp on the alarm body while pulling the power harness free.